1. Field of the Invention
The present invention relates to a developing apparatus, a cleaning apparatus and a developer transporting screw used therefor, which are used for an image forming apparatus of an electrophotographic type such as a copy machine and a printer. More specifically, the present invention relates to a developing apparatus for suppressing the movement of a developer in the midst of transportation between screws arranged vertically so that the developer may be stirred sufficiently to prevent the occurrence of fog on the image and the smoke of toner, a developer transporting screw therefor or a cleaning apparatus for suppressing the occurrence of the smoke of toner by using the developer transporting screw. The present invention further relates to a developing apparatus in which only the fully stirred and charged developer is transported into a development zone thereby obtaining an excellent image in a stable manner without occurrence of fog or unevenness.
2. Related Art
In the developing apparatus used for a copier or the like, when a developer in an insufficient stirred state or in a charge-short state is supplied to a development roller, the fog or unevenness of the image occurs.
Various devices have been made to solve the problem. One example is described in Japanese Unexamined Patent Publication No. Hei 5-333691. In this developing apparatus, upper and lower augers (screws) 82, 85 are arranged in such a manner that a barrier plate 84 is put therebetween in parallel in order to their transporting directions are opposed to each other, as shown in FIG. 29. A developer is supplied, while being circulated in a direction as indicated by the arrow, to a developer carrier (a development roller) 87 provided adjacent to the auger to develop an electrostatic latent image on a photosensitive medium through the developer carrier 87. In this developing apparatus, the upper auger 82 supplies developer to the developer carrier 87, and the lower auger 85 recovers developer from the developer carrier 87.
The barrier plate 84 is provided to prevent the movement of developer in the midst of transportation from the upper auger 82 to the lower auger 85 in the circulation of developer. The reason is that when the movement of developer between the augers in the midst of transportation occurs, the developer not sufficiently stirred is supplied to the developer carrier 87.
However, in the aforementioned conventional developing apparatus, since the upper auger 82 and the lower auger 85 have the same shape and rotate at similar rotational speed, pressure applied by the upper auger 82 to the lower auger 85 is the same as that of applied by the lower auger 85 to the upper auger 82. There occurs, what is called, the lowering of developer. That is, developer moves to the lower auger 85 in the midst of being transported by the upper auger 82 by gravity. When the lowering of developer occurs, toner newly supplied is supplied to the developer carrier (the development roller) 87 in the insufficient charged state without being sufficiently stirred by the upper auger 82. Therefore, the fog on the image and the smoke of toner may occur.
Further, since the barrier plate 84 is provided, the transfer of developer between the auger 82 and the auger 85 at opposite ends is impeded, and the developer may stay at the transfer portion of the developer. When developer stays at the portion, the developer is not well circulated and the deviation of developer transported by the augers 82 and 85 may occur. When the deviation of developer occurs in the auger 82, the developer is not evenly supplied from the auger 82 to the developer carrier 87, there arises the problem of the deterioration of image quality due to the unevenness or fog.
The augers are used also in the cleaning apparatus for removing developer which remains on the image carrier after transfer. However, when the conventional auger rotates, not only pressure in an axial direction of developer generates but also the outward pressure generates. Therefore, developer in the cleaning apparatus is released outward while being transported axially to generate the smoke of toner.
A further conventional developing apparatus is described in Japanese Examined Patent Publication No. Hei 4-9304. In this developing apparatus, shafts of a first auger (a transporting screw) 97 and a second auger 98 are projected from a development tank 92, and a mixing blade 91 is provided between the shafts to form a preliminary stirring chamber 93. Developer is sufficiently stirred by the blade 91 in the preliminary stirring chamber 93, charged and then supplied into the development tank 92.
However, there is a problem that the apparatus becomes larger in size. Because the preliminary stirring chamber 93 for sufficiently stirring developer to charge it is required this side of the development tank 92. Particularly, there arises a problem when the apparatus is used for a color image forming apparatus provided with a number of developing apparatuses.